Post-surgical recurrence or development of metastatic disease in patients with malignant melanoma is associated with a very high level of mortality. Unfortunately, the efficacy of adjuvant therapy with recombinant interferon alpha (IFN1) is limited by the development of strategies that allow the tumor to evade the anti- proliferative and anti-angiogenic effects of IFN1. Such strategies are likely acquired early in melanoma development/progression to circumvent the anti-tumorigenic effects of endogenous IFN1. Our laboratory made the seminal discovery that phosphorylation-dependent degradation of the IFNAR1 subunit of IFN1 receptor is a key mechanism by which the sensitivity to IFN1 is regulated. Moreover, preliminary data reveal that melanoma cells can accelerate IFNAR1 degradation and inhibit IFN1 signaling by secreting inflammatory cytokines such as interleukin 1 (IL1). These cytokines induce the specific IFNAR1 phosphorylation that leads to recruitment of the Trcp E3 ubiquitin ligase and subsequent ubiquitination and degradation of IFNAR1. Activation of p38 kinase appears to play a central role in the degradation of IFNAR1 via this pathway. Importantly, p38 kinase activation and IFNAR1 phosphorylation/downregulation also occur in normal melanocytes in response to ultraviolet light (UV), implicated in the etiology of malignant melanoma. Together, these data have led us to hypothesize that development and progression of malignant melanoma is abetted by UV and/or inflammatory cytokine-induced p38 kinase-dependent degradation of IFNAR1. The consequent reduction in IFN1/2 sensitivity would allow tumor cells to evade the anti-proliferative and pro- apoptotic effects of IFN1/2. To test this hypothesis, we will: (i) determine whether inflammatory cytokines regulate the sensitivity of malignant melanomas to IFN1 therapy by inducing p38-mediated degradation of IFNAR1, and evaluate the role of accelerated IFNAR1 degradation in malignant melanoma development (ii) and progression (iii). Multiple complementary in vitro and in vivo approaches will be utilized, including unique mouse models, melanomas expressing IFNAR1 variants that are resistant to this degradation pathway, and comprehensive panels of human melanoma cell lines and clinical samples. We anticipate that these studies will highlight an important role for UV-induced and/or inflammation-mediated degradation of IFNAR1 in melanoma etiology and pathogenesis, thereby revealing novel aspects of melanomagenesis that could be targeted for early intervention. Moreover, these studies will investigate the molecular mechanisms underlying the resistance of established melanoma to therapeutic IFN1, thereby providing essential insight for the development of novel targets for increasing the therapeutic efficacy of IFN1.